The cellular events leading to the pathogenesis of neurofibrillary pathology (NFP) in Alzheimer's disease (AD) are poorly understood. This proposal focuses on the pathogenic mechanisms at the cellular and subcellular level and focuses on immunoelectron microscopy of the lesions in well fixed brain tissue, obtained from either biopsy or rapid autopsy. We propose three studies which will provide significant new insights into the pathogenesis of NFP. First, the morphogenesis of abnormal filaments in the dystrophic neurites characteristic of AD will be studied by the accurate localization of cytoskeletal proteins in the different types of abnormal and normal filaments. In conjunction, studies will establish whether there is structural continuity between the abnormal filaments and the cytoskeleton. Further morphometric analysis will be used to determined the organization of the normal and abnormal filaments and whether neuropil threads originate from neurofibrillary tangle bearing neurons. Second, we will determine the chemical association of tubulin and the neurofilament heavy subunit with paired helical filaments (PHF). Identification of these proteins in enriched PHF fractions as well as quantification will be used to establish whether both are chemically integral PHF components. In a series of reconstitution experiments using neurofilament and microtubule proteins we will attempt to understand the factors responsible for abnormal filament formation in AD based on protein interaction. Finally, we will study the aged or alcohol treated rat as a model of NFP. Immunocytochemistry at the light and electron microscopic levels will be used to characterize the changes seen in rats and compared to NFP in AD. These results will serve as the prelude to protein chemical characterization of NFP in the rat model. These experiments are expected to provide significant information on a) the structural role the cytoskeleton plays in NFP formation as well as the interaction of normal and abnormal structures; b) identification of NFH and tubulin as components of NFP as well as their importance in abnormal filament formation; and c) development of a model to study NFP.